U.S. patent application number 10/238087 was filed with the patent office on 2003-01-16 for method for forming thin film, spheroid coated with thin film, light bulb using the spheroid and equipment for film formation.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Hashimoto, Naotaka, Kitai, Takahiro, Omata, Yuuji, Suemitsu, Toshiyuki, Yokoyama, Masahide.
Application Number | 20030012886 10/238087 |
Document ID | / |
Family ID | 14327592 |
Filed Date | 2003-01-16 |
United States Patent
Application |
20030012886 |
Kind Code |
A1 |
Omata, Yuuji ; et
al. |
January 16, 2003 |
Method for forming thin film, spheroid coated with thin film, light
bulb using the spheroid and equipment for film formation
Abstract
The present invention provides a method for forming thin films,
wherein thin films with a uniform thickness can be formed on
substrates as objects such as spheroids, even when the films are
formed by conventional film-formation methods using an incident
particle beam coming from a specific direction (e.g., evaporation
and sputtering). In the method, thin films are formed on substrates
such as spheroids with an incident particle beam coming from a
particle source located in a specific direction by performing a
spin motion together with a swing motion. The spin motion is a
rotation of the substrate at a constant angular velocity about the
spheroidal axis. The swing motion is a rotational oscillation of
the same substrate for rotationally oscillating the axis at a
constant cycle in one surface, where the center of the rotational
oscillation is in the vicinity of the midpoint between two focal
points on the axis of the spheroid. As a result, thin films with a
uniform thickness in both the peripheral direction of the substrate
and in the rotational axis direction of the spin motion can be
formed even on substrates including spheroids.
Inventors: |
Omata, Yuuji; (Toyonaka-shi,
JP) ; Hashimoto, Naotaka; (Takatsuki-shi, JP)
; Yokoyama, Masahide; (Hirakata-shi, JP) ;
Suemitsu, Toshiyuki; (Minoo-shi, JP) ; Kitai,
Takahiro; (Hirakata-shi, JP) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
Kadoma-shi
JP
|
Family ID: |
14327592 |
Appl. No.: |
10/238087 |
Filed: |
September 9, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10238087 |
Sep 9, 2002 |
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09537622 |
Mar 29, 2000 |
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6472022 |
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Current U.S.
Class: |
427/424 ;
427/425; 427/583; 427/595; 428/34.4 |
Current CPC
Class: |
C23C 14/505 20130101;
Y10T 428/8305 20150401; H01J 9/20 20130101; H01K 3/005 20130101;
Y10T 428/131 20150115; Y10T 428/2991 20150115 |
Class at
Publication: |
427/424 ;
427/425; 427/583; 427/595; 428/34.4 |
International
Class: |
F16L 009/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 1999 |
JP |
11-102442 |
Claims
What is claimed is:
1. A method for forming a thin film on a substrate comprising a
spheroid with an incident particle beam coming from a particle
source located in a specific direction when viewed from the
substrate, wherein the substrate is subjected to a spin motion
together with a swing motion, in which the spin motion is a
rotation of the substrate at a constant angular velocity about the
spheroidal axis and the swing motion is a rotational oscillation of
the same substrate for rotationally oscillating the axis at a
constant cycle in one surface, and the center of the rotational
oscillation is in the vicinity of a midpoint between two focal
points on the axis of the spheroid.
2. The method for forming a thin film according to claim 1, wherein
the swing motion is performed to get the part of the spheroid below
the midpoint of the axis positioned away from the particle source
when the upper part of the same axis approaches the particle
source.
3. The method for forming a thin film according to claim 1, wherein
the particle source is a flat plate and the swing motion is
performed to rotationally oscillate the axis at a constant cycle in
a surface perpendicular to the flat plate surface.
4. The method for forming a thin film according to claim 1, wherein
the rotational angular velocity of the rotational oscillation of
the swing motion is varied continuously.
5. The method for forming a thin film according to claim 1, wherein
the rotational oscillation is varied intermittently in the swing
motion by setting plural stationary positions within the rotational
oscillation range and stationary times at the respective stationary
positions.
6. The method for forming a thin film according to claim 1, wherein
the film formation method comprises sputtering or evaporation.
7. The method for forming a thin film according to claim 6, wherein
the thin film is at least either an infrared reflection film or a
frost film.
8. The method for forming a thin film according to claim 1, wherein
the substrate comprising a spheroid is a light bulb.
9. The method for forming a thin film according to claim 8, wherein
the center of the rotational oscillation of the swing motion is in
the vicinity of the longitudinal center of the filament portion of
the light bulb.
10. A spheroid coated with a thin film of an incident particle beam
coming from a particle source located in a specific direction when
viewed from the spheroid, wherein the thin film is formed on the
spheroid by performing a spin motion together with a swing motion
and has a thickness distribution substantially uniform in the
rotational direction of the spin motion and also in the rotational
oscillation direction of the swing motion, in which the spin motion
is a rotation of the substrate at a constant angular velocity about
the spheroidal axis and the swing motion is a rotational
oscillation of the same spheroid for rotationally oscillating the
axis at a constant cycle in one surface, and the center of the
rotational oscillation is in the vicinity of the midpoint between
two focal points on the axis of the spheroid.
11. The spheroid according to claim 10, wherein the swing motion is
performed to get the part of the spheroid below the midpoint of the
axis positioned away from the particle source when the upper part
of the same axis approaches the particle source.
12. The spheroid according to claim 10, wherein the particle source
is a flat plate and the swing motion is performed to rotationally
oscillate the axis at a constant cycle in a surface perpendicular
to the flat plate surface.
13. The spheroid according to claim 10, wherein the thin film is
formed by sputtering or by evaporation.
14. The spheroid according to claim 10, wherein the thin film is at
least either an infrared reflection film or a frost film.
15. The spheroid according to claim 10, wherein the spheroid is a
light bulb.
16. The spheroid according to claim 15, wherein the center of the
rotational oscillation of the swing motion is in the vicinity of
the longitudinal center of the filament portion of the light
bulb.
17. A light bulb comprising a spheroid coated with a thin film
according to any one of claims 10 to 16.
18. Film formation equipment for forming a thin film on a substrate
comprising a spheroid with an incident particle beam coming from a
particle source located in a specific direction when viewed from
the substrate, the equipment comprising a rotational mechanism for
performing a spin motion together with a swing motion, in which the
spin motion is a rotation of the substrate at a constant angular
velocity about the spheroidal axis and the swing motion is a
rotational oscillation of the same substrate for rotationally
oscillating the axis at a constant cycle in one surface, and the
center of the rotational oscillation is in the vicinity of the
midpoint between two focal points on the axis of the spheroid.
19. The equipment according to claim 18, further comprising a high
frequency sputtering or direct current sputtering member for
forming the thin film.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for forming
infrared reflection films used for light sources such as
incandescent lamps or tungsten-halogen lamps. The present invention
relates also highly efficient light sources as light bulbs provided
with the infrared reflection films.
BACKGROUND OF THE INVENTION
[0002] `Journal of Illuminating Engineering Society`, July 1980 (p.
197-203) or some other documents have suggested methods for
providing low power incandescent lamps and tungsten-halogen lamps.
For this purpose, light bulbs are coated with infrared reflection
films to substantially pass only visible light that is selected
from light beams emitted from filament portions of the light
bulbs.
[0003] In this method, a maximum proportion of the infrared
reflection light, which appears to compose 70-80% of the radiation
energy, can be reflected inside of the light bulb. The reflected
light is focused on the filament coil portion to heat the same
portion. Since the filament coil portion is reheated in this
manner, the consumed power is reduced by 20-30% in comparison with
a conventional light bulb when the illuminance (total value of
luminous flux) from the filament portions is equivalent.
[0004] Such an infrared reflection film includes an interference
multilayer film having a laminate of transparent dielectric thin
films with high refractive index and low refractive index. The
interference multilayer film decreases infrared rays escaping as
heat rays from the light bulb, and it selectively passes visible
light only, so that the infrared rays can be reflected
effectively.
[0005] To form infrared reflection films with the best uniformity
on three-dimensional objects (in many cases, spheroids) such as
light bulbs, various methods such as CVD, evaporation or sputtering
are used.
[0006] In the above-mentioned interference multilayer films, the
films are required to be coated with an accurate thickness while
they have desired refractive indices. Evaporation and sputtering
are useful in forming thin films with a controlled thickness on
conventional flat substrates. However, the methods are not suitable
for forming thin films with a uniform thickness on
three-dimensional objects including spheroids such as light
bulbs.
[0007] In a case of a three-dimensional object, generally, the
distance from the object to either an evaporation source or a
sputtering target can vary. Moreover, the other side (the side away
from the evaporation source or the target) of the object should be
also coated with a film. As a result, the film has a considerably
uneven thickness, and the multilayer film cannot show its
functions, and the efficiency of the infrared ray reflection will
deteriorate.
[0008] Furthermore, visible light of a wavelength to be transmitted
is reflected excessively due to the film with uneven thickness. As
a result, problems such as coloration and color unevenness will
occur in the electric light source.
[0009] CVD is used for forming thin films by using starting
molecules which are supplied as a gas flow from substantially all
directions rather than a specific direction. This method can
provide comparatively uniform film thickness without any special
difficulties. However, CVD also presents several problems, for
example, the absolute value of the film thickness cannot be
controlled sufficiently. In addition, the object will be heated
inevitably, and the material gasses or the conditions should be
changed for the respective films composing a laminate.
SUMMARY OF THE INVENTION
[0010] To solve the problems, the present invention provides a
method for forming thin films with a uniform thickness on
substrates including spheroids even by film-forming methods such as
evaporation or sputtering. In evaporation or sputtering, incident
particles as film materials will be supplied from a specific
direction. The present invention also provides a spheroid coated
with a film of the method, a light bulb including the spheroid and
equipment for film formation.
[0011] In order to achieve the purpose, the method for forming thin
films according to the present invention includes forming a thin
film on a substrate including a spheroid with an incident particle
beam coming from a particle source located in a specific direction
when viewed from the substrate. In this method, a spin motion and a
swing motion are performed together. The spin motion is a rotation
of the substrate at a constant angular velocity about the
spheroidal axis. Here, `spheroidal axis` refers to the central axis
of the rotation of a spheroid. The swing motion is a rotational
oscillation of the same substrate for rotationally oscillating the
axis at a constant cycle in one surface, where the center of the
rotational oscillation is in the vicinity of the midpoint between
two focal points on the axis of the spheroid.
[0012] In the method using a spin motion and a swing motion
together, a thin film that has a uniform thickness in the
peripheral direction of the substrate and in the rotational
direction of the spin motion can be formed even if the substrate
comprises a spheroid.
[0013] It is preferable in the method that the swing motion is
performed to get the part of the substrate below the midpoint of
the axis positioned away from the particle source when the upper
part of the same axis approaches the particle source, so that the
uniformity of the thin film in the rotational axis direction is
further assured.
[0014] It is also preferable that the particle source is a flat
plate and the swing motion is performed to rotationally oscillate
the axis at a constant cycle in a surface perpendicular to the flat
plate surface, so that the uniformity of the thin film in the
rotational axis direction is further assured.
[0015] It is preferable that the rotational angular velocity of the
rotational oscillation of the swing motion is varied continuously,
so that the rotational velocity of the swing motion can be set to
be suitable for the distance distribution between the substrate
surface and the particle source surface.
[0016] It is preferable that the rotational oscillation is varied
intermittently by setting plural stationary positions within the
rotational oscillation range and also stationary times at the
respective positions, so that the swing motion can be performed
easily.
[0017] It is preferable that the thin film is formed by either
sputtering or evaporation.
[0018] It is preferable that the thin film is at least one selected
from the group consisting of an infrared reflection film and a
frost film.
[0019] It is also preferable that the substrate including a
spheroid is a light bulb.
[0020] It is preferable that the center of the rotational
oscillation of the swing motion is in the vicinity of the
longitudinal center of the filament portion of the light bulb.
[0021] A spheroid of the present invention is coated with a thin
film, and the thin film is formed with an incident particle beam
coming from a particle source located in a specific direction when
viewed from the spheroid as an object. The spheroid is subjected to
a spin motion together with a swing motion in order to form a thin
film thereon. The spin motion is a rotation of the spheroid at a
constant angular velocity about the spheroidal axis. The swing
motion is a rotational oscillation of the same spheroid for
rotationally oscillating the axis at a constant cycle in one
surface, where the center of the rotational oscillation is in the
vicinity of the midpoint between two focal points on the axis of
the spheroid. The thin film has a uniform thickness at least in the
rotational direction of the spin motion and also in the rotational
oscillation direction of the swing motion.
[0022] The spheroid coated with the thin film is useful for light
bulbs due to the uniformity in the film thickness.
[0023] It is preferable in the spheroid that the swing motion is
performed to get the part of the spheroid below the midpoint of the
axis positioned away from the particle source when the upper part
of the same axis approaches the particle source, so that the
uniformity of the thin film in the rotational axis direction is
further assured.
[0024] It is also preferable that the particle source is a flat
plate and the swing motion is performed to rotationally oscillate
the axis at a constant cycle in a surface perpendicular to the flat
plate surface, so that the uniformity of the thin film in the
rotational axis direction is further assured.
[0025] It is preferable that the thin film is formed by sputtering
or by evaporation.
[0026] It is also preferable that the thin film is at least one
selected from the group consisting of an infrared reflection film
and a frost film.
[0027] It is preferable that the spheroid is a light bulb.
[0028] It is preferable that the center of the rotational
oscillation of the swing motion is in the vicinity of the
longitudinal center of the filament portion of the light bulb.
[0029] A light bulb of the present invention includes a spheroid
coated with a thin film. The film on the light bulb is
substantially uniform in thickness, since it is formed with an
incident particle beam coming from a specific direction while the
spheroid (light bulb) is subjected to a swing motion together with
a spin motion. In order to meet the requirement for the uniformity,
the film thickness on the spheroidal substrate in a range of
.+-.60.degree. from the vertical angle (see the upper right-hand in
the graph of FIG. 1) is at least 88% of the maximum film thickness,
i.e., .+-.6% to the medium value. When the thin film is a laminate
comprising transparent dielectric thin films differing in their
refractive indices, the light bulb can be prevented from being
colored or having color unevenness, and the energy will be saved
considerably.
[0030] Film-formation equipment of the present invention is used to
form thin films having a uniform thickness on substrates comprising
spheroids with an incident particle beam coming from a particle
source located in a specific direction when viewed from the
substrates. The equipment is provided with a rotational mechanism
to perform a spin motion together with a swing motion. The spin
motion is a rotation of the spheroid at a constant angular velocity
about the spheroidal axis. The swing motion is a rotational
oscillation of the same spheroid for rotationally oscillating the
axis at a constant cycle in one surface, where the center of the
rotational oscillation is in the vicinity of the midpoint between
two focal points on the axis of the spheroid.
[0031] It is preferable that the equipment uses RF (radio
frequency) sputtering or DC (direct current) sputtering in the film
formation process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a graph to show a relationship between the
vertical angle on a light bulb and the thickness of a film, where
the film is formed by the method in a first embodiment of the
present invention.
[0033] FIG. 2 is a graph to show a relationship between the
rotational angle along the periphery of a bulb and the film
thickness, where the thin film is formed by the method in the first
embodiment of the present invention.
[0034] FIGS. 3A and 3B are schematic views to show light bulbs to
be coated with thin films by the methods of the present
invention.
[0035] FIG. 4 is a graph to exemplify a swing motion in film
formation according to the first embodiment.
[0036] FIG. 5 is a graph to show a relationship between the
vertical angle on a light bulb and the thickness of a film, where
the film is formed by the method in a second embodiment of the
present invention.
[0037] FIG. 6 is a graph to exemplify a swing motion in film
formation according to the second embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Embodiments of the present invention are explained
specifically below by referring to FIGS. 1-6. FIGS. 3A and 3B
exemplify the configurations of light bulbs used in the
embodiments. Both a light bulb 1 in FIG. 3A and a light bulb 4 in
FIG. 3B include spheroids. Filaments in the light bulbs focus
infrared rays. Since the length of the filaments is restricted in
view of energy-saving, a typical light bulb includes a spheroid
having a proper ratio of the long axis to the short axis.
Hereinafter, the figure of the light bulb 1 is referred to as
"spheroid A" while that of the light bulb 4, which is a substantial
sphere, is referred to as "spheroid B".
[0039] The light bulbs have filaments 3, 6 and electrode terminals
2, 5 respectively. "P" in FIG. 3A indicates a midpoint between two
focal points (Q and R) on the rotational axis of the spheroid. FIG.
3B also has a similar midpoint though it is not shown. The midpoint
P is typically located on a filament coil in the longitudinal
direction.
[0040] First Embodiment
[0041] In this embodiment, an SiO.sub.2 thin film was formed on a
light bulb with RF sputtering. The target was a flat plate 200 mm
in width and 900 mm in length.
[0042] A spin motion and a swing motion were performed together to
prevent the film on the light bulb from having uneven thickness.
The spin motion is a rotation of the light bulb at a constant
angular velocity about the spheroidal axis. The swing motion is a
rotational oscillation of the same light bulb for rotationally
oscillating the axis at a constant cycle in one surface, where the
center of the rotational oscillation is the midpoint P. In the spin
motion, the spheroid rotates about the axis of the filament at a
regular angular velocity of 100 rpm.
[0043] Though the spin motion can provide a thin film with a
thickness uniform in the rotational direction, a swing motion
should be carried out together with the spin motion in order to
provide a film with a thickness uniform in the rotational axis
direction.
[0044] The swing motion is a rotational oscillation at a constant
cycle, where the spheroidal axis undulates at .+-.60 degrees from
the midpoint P in a surface parallel to the flat plate target (see,
the upper right-hand in the graph of FIG. 1). The swing motion is
not effective if the rotational amplitude surface is parallel to
the target surface. In the First Embodiment, the rotational axis of
the spheroid is set to move in a surface perpendicular to the
target surface. More specifically, the axis oscillates rotationally
so that the part of the spheroid below the midpoint P of the
spheroidal axis is positioned away from the flat plate target when
the part above the midpoint P of the same axis approaches the flat
plate target during the swing motion.
[0045] The rotational velocity of the swing motion should be set
corresponding to the distance distribution between the substrate
surface and the flat plate target surface, since the distance
depends on the spheroidal shape in the rotational axis direction of
the light bulb (an object). When the spheroid is made to be a
substantial sphere (spheroid B), the swing motion substantially
becomes a simple harmonic oscillation.
[0046] In the First Embodiment, one cycle of the swing motion is 20
seconds, and the swing angle of the rotational axis shifts in one
cycle as indicated in FIG. 4 (hereinafter, it is called "a
continuous swing mode"). The solid line in FIG. 4 indicates a
continuous swing mode for a light bulb with a spheroid A, while the
broken line indicates the same for a light bulb with a spheroid
B.
[0047] FIGS. 1 and 2 shows results of measurement on the film
thickness distribution for the spheroids A and B, where a spin
motion was performed alone or together with a swing motion. The
distance between the flat plate target surface and the rotational
axis of spheroids (light bulb filaments) was set to be 90 mm.
[0048] FIG. 1 shows the thickness distribution of a film formed on
spheroids of light bulbs in the rotational axis direction. FIG. 1
shows also a measurement result as a comparative example obtained
by forming a film using only a spin motion but not a swing motion.
FIG. 2 shows a thickness distribution of a film in the direction of
the cross-sectional circumferential direction (spin rotational
direction) perpendicular to the rotational axis.
[0049] The ordinate in FIG. 1 indicates thickness (nm) of an
SiO.sub.2 film. The abscissa indicates positions of a light bulb
surface corresponding to vertical angles (elevation angle) of a
surface that is perpendicular to the rotational axis of a spheroid
comprising the midpoint P. For the vertical angle, the direction
inverse to the light bulb terminals is determined to be the plus
direction, while the light bulb terminal side is determined to be
the minus direction (see upper right-hand in FIG. 1).
[0050] The ordinate in FIG. 2 indicates thickness (nm) of an
SiO.sub.2 film. The abscissa indicates positions on the light bulb
periphery on a surface perpendicular to the rotational axis of a
spheroid including the midpoint P. The zero-degree direction is the
position where a mount is provided to the filament on the
rotational axis. The angles are displayed by determining the
counterclockwise direction as the plus direction about the
rotational axis relative to the zero-degree when viewed from the
top of the light bulb (right-center in FIG. 2).
[0051] FIGS. 1 and 2 show that films can be formed on light bulbs
with a substantial uniformity in both the vertical and horizontal
directions when a swing motion is performed together with a spin
motion.
[0052] The measurement result in FIG. 1 shows that additional use
of a swing motion is remarkably effective when compared with the
result obtained by using only a spin motion. The problem of uneven
thickness of the thin film formed on a bulb cannot be solved by
using a spin motion alone, especially when the thin film is formed
with an incident particle beam coming from a particle source
located in a specific direction when viewed from the object (e.g.,
RF sputtering).
[0053] Second Embodiment
[0054] In the Second Embodiment, an SiO.sub.2 thin film was formed
on a light bulb surface by using RF sputtering as in the First
Embodiment. This embodiment is distinguishable from the First
Embodiment in that the swing motion is not a continuous motion as
shown in FIG. 4 but an intermittent motion as shown in FIG. 6
(hereinafter, it is called "a step-swing mode").
[0055] In a step-swing mode in FIG. 6, an oscillation angular range
of a rotational oscillation in a swing motion of a predetermined
cycle is divided to be set as plural stationary angles (.theta.n),
and stationary times (tn) for the respective stationary angular
positions are also set. More specifically, the rotational motion of
the swing is set as (.theta.1, t1) . . . (.theta.n, tn) within the
range of the amplitude angles. The step-swing mode can be provided
in a simple manner compared to the continuous swing mode described
in the First Embodiment.
[0056] In this embodiment, n=5, and the rotational angular range of
the swing amplitude is set to be .+-.45 degrees to the medium
value. As shown in FIG. 6, the cycle of the rotation is set with a
step-swing mode, in which (.theta.1, t1)=(-45.degree., 5.3
seconds); (.theta.2, t2)=(-30.degree., 3.2 seconds); (.theta.3,
t3)=(0.degree., 2.0 seconds); (.theta.4, t4)=(+30.degree., 3.2
seconds); and (.theta.5, t5)=(+45.degree., 5.3 seconds).
[0057] In the swing motion shown in FIG. 6, rotation is performed
from .theta.1 to .theta.5, and the rotation returns from .theta.5
to .theta.1, so one cycle is about 28 seconds. The angular velocity
for moving between the respective stationary angular positions can
be constant or not. In the Second Embodiment, the velocity for
moving between the respective stationary angular positions is
substantially constant, and the time required for the move is short
(within one second per step) when compared to the stationary time
(tn) at each stationary angular position.
[0058] FIG. 5 shows a comparison between an example using the
step-swing mode in addition to a spin motion, and a comparative
example using a spin motion alone. Both the example and comparative
example include SiO.sub.2 thin films formed on light bulbs by using
RF sputtering as in the First Embodiment. Here, light bulbs having
spheroid A were used. The target was a flat plate 200 mm in width
and 900 mm in length. In the spin motion, the spheroid rotates
about the axis of the filament at a regular angular velocity of 100
rpm.
[0059] The ordinate and abscissa correspond to those in FIG. 1.
FIG. 5 shows that a step-swing mode can provide a uniform film
thickness as in the case of a continuous swing mode. The effect is
further remarkable when compared with a comparative example of a
film formed by using a spin motion alone.
[0060] As mentioned above, the film-forming methods in the
embodiments provide thin films with a uniform thickness. Therefore,
the method for forming films of the present invention is useful in
forming interference infrared reflection multilayer films or frost
films on light bulbs. Such multilayer films comprise laminates of
transparent dielectric multilayer films differing in the refractive
indices.
[0061] A 90W tungsten-halogen lamp including a light bulb having a
spheroid was prepared by forming an infrared reflection thin film
on the spheroid by using a method in the present invention. This
lamp was used for a comparison with a tungsten-halogen lamp having
the identical total value of luminous flux (1600 lumen) prepared
without using the method of the present invention. The efficiency
of the present invention (lm/W) was improved by about 30%.
[0062] Frost films to soften the glare of the light bulb also were
formed uniformly as the outermost layer on the light bulb.
[0063] RF sputtering was used for forming thin films in the
embodiments. The film-forming method is not limited thereto as long
as the thin films are formed with an incident particle beam coming
from a particle source located in a specific direction when viewed
from the substrates. Equivalent effects are obtainable in any other
general-purpose sputtering such as DC sputtering, or various kinds
of evaporation.
[0064] Thin films in the above-identified embodiments can be formed
by using film-formation equipment having a rotational mechanism for
performing a spin motion together with a swing motion, and by
combining the film-forming method with conventional evaporation or
sputtering.
[0065] Consequently, according to the present invention, a thin
film with a uniform thickness can be formed with accurate control
on a substrate even when incident sputtered particles are supplied
from only a specific direction as in a conventional method such as
evaporation and sputtering, or even when the substrate comprises a
spheroid such as a light bulb.
[0066] As a result, even a laminate film comprising transparent
dielectric films with different refractive indices can be formed
uniformly with accurate control on a curved surface of a light
bulb, an efficient and energy-saving light bulb can be
manufactured, and the light bulb is protected from light coloration
or color unevenness.
[0067] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof The embodiments disclosed in this application are to be
considered in all respects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims
rather than by the foregoing description, all changes that come
within the meaning and range of equivalency of the claims are
intended to be embraced therein.
* * * * *